1. Field of the Invention
This invention relates in general to a direct access storage device (DASD), and more particularly to an active micromechanical air valve for providing pressure control and method for making the same.
2. Description of Related Art
Conventional magnetic storage devices include a magnetic transducer or xe2x80x9cheadxe2x80x9d suspended in close proximity to a recording medium, e.g., a magnetic disk having a plurality of concentric tracks. The transducer is supported by an air bearing slider mounted to a flexible suspension. The suspension, in turn, is attached to a positioning actuator. During normal operation, relative motion is provided between the head and the recording medium as the actuator dynamically positions the head over a desired track. The relative movement provides an air flow along the surface of the slider facing the medium, creating a lifting force. The lifting force is counterbalanced by a predetermined suspension load so that the slider is supported on a cushion of air. Air flow enters the leading edge of the slider and exits from the trailing end. The head resides toward the trailing end, which tends to fly closer to the recording surface than the leading edge.
The recording medium holds information encoded in the form of magnetic transitions. The information capacity, or areal density, of the medium is determined by the transducer""s ability to sense and write distinguishable transitions. An important factor affecting areal density is the distance between the transducer and the recording surface, referred to as the fly height. It is desirable to fly the transducer very close to the medium to enhance transition detection. Some fly height stability is achieved with proper suspension loading and by shaping the air bearing slider surface (ABS) for desirable aerodynamic characteristics.
Under some circumstances it is desirable to change the flying height of the slider holding the magnetic recording head in a disk drive. One primary reason is that the areal density of data can be increased when the recording head is close to the disk surface. That is because magnetic recording is a xe2x80x9cnear-fieldxe2x80x9d process; in other words, writing by the write head and reading by the read head occur in close proximity to the disk. This leads to an exponential dependence of the field on the spacing between the head and disk and, consequently, areal density.
Hard drive manufactures are starting to incorporate proximity recording type sliders in drives in order to achieve higher storage densities. The proximity recording slider is designed to maintain a small area near the read-write element in constant contact or near-contact with the disk, and thus enabling smaller bit size and ultimately larger storage densities.
This approach to increasing storage density puts considerable amount of strain on controlling wear at the slider-disk interface, because a slight variation in contact load and contact area could greatly affect the drive survivability. Slider-disk contact results in lubricant depletion and degradation, wear of both surfaces, generation of wear particles, stick-slip, etc. All these phenomena affect magnetic performance of the disk drive, e.g., through jitter, as well as its durability. Nevertheless, as mentioned above, a contact slider is key for high-density magnetic recording.
Thus, maintaining a stable and reliable interface is required to ensure proper functioning of a disk drive. For example, if the spacing between a write head and the magnetic disk is too large, the head""s fringing field will be too weak to record data on the disk. Also, the read-back signal registered by a read head (usually, a magnetoresistive head integrated with the write head) will be reduced and data errors may occur. On the other hand, very low head-disk spacing may improve magnetic performance, but can lead to mechanical wear of the head and disk, substantially reducing the lifetime of both.
Of course, as areal density of data increases, the tolerances in the head-disk spacing or the flying height must be reduced. This places significant constraints on both head and disk parameters. Since typical disks can be out of flatness by as much as 20-50 nm (nanometers) and the slider flies at a height of less than 30 nm the compliance of the head and suspension must be sufficient to compensate for this large motion while tracking the disk surface.
The prior art air bearing technology used in disk drives offers a large number of different designs. They were developed to satisfy somewhat different criteria, and over the years they have become more elegant, with improved performance allowing decreased head-disk spacing. Some of the requirements for specific air bearing designs include rapid take-off, close compliance to the disk""s surface, stable flying and minimal variation of flying height of the slider at different radial positions on the disk. The last item is important since the relative velocity of the head over the disk can change by as much as a factor of 2 from the inside to the outside diameter of a typical magnetic recording disk. The different velocities alter the air pressure under the slider and result in changes in flying heights than can impact the head""s ability to read and write properly. Changes in ambient pressure also affect the flying height. Thus, the flying height in a disk drive operating in a low pressure environment, e.g., on-board an airplane, is different than the flying height in a disk drive operating at standard atmospheric pressure. Finally, with the widespread use of rotary actuators in disk drives, the air bearing must be able to fly in a stable manner over a range of azimuthal orientations (20-25 degrees) of the head with respect to the disk.
As can be seen, the fly height spacing control for a read/write element is a critical parameter in a hard disk storage device. A near contact spacing gap during writing and reading would greatly enhance the signal to noise ratio and allow the increase to higher Arial bit densities. However, a constant near contact fly height would have greater wear and tribologic effects between the head and the disk over time. It would be desirable to limit the contact to the times when recording is taking place while maintaining a low flying height, e.g., on the order of 5-50 nm at all other times.
The ability to have the head contact the disk surface-on-demand (SOD) with minimal impact to current head manufacturing is desirable. The majority of the time, the slider is neither reading nor writing on a disk. Accordingly, the head can be flown higher during this inactive time to provide greater spacing between the head and the disk to minimize wear. Previous work have sought to achieve this by building a member that deforms the trailing edge of the slider.
Other changes to the fly height can be accomplished through changing the pressure inside the drive enclosure. A portion of the air would be pumped out of the drive through a valve. This valve would maintain a sub-ambient pressure for the drive to operate.
W. K. Schomburg disclose in the Journal of Micromechanical Microengineering, 2, 184 (1992), a large, passive air valve for use as a pressure release valve. The Schomburg structure requires a 450xc2x0 C. anneal to relieve stress in the stiff bridge material which was made of titanium. Because this similar valve is passive and is hundreds of microns in diameter, a large differential pressure is required to actuate the valve. In addition, the valve would take many seconds for a measurable pressure change between the two sides of the membrane to occur.
Moreover, the head environment demands much more stringent scaling requirements and temperature limits during the processing of the head. For example, in order to prevent alteration of the read element, a 200xc2x0 C. thermal budget is imposed. Moreover, an active valve is required to accomplish the goals of controlling the fly height of a head.
It can be seen that there is a need for an active micromechanical air valve for fly height control of an air bearing slider and method for making the same.
It can also be seen that there is a need for an active micromechanical air valve that meets the processing requirements of head production processes as well as the scaling requirements.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses an active micromechanical air valve for air bearing surface pressure control of an air bearing slider and method for making the same.
The present invention solves the above-described problems by providing a micromechanical air valve that will control the air flow to the ABS or air flow to/from the drive enclosure, thus altering the fly height. When the valve is activated, air can pass through a valve and down etched air tubes that are open to the ABS.
An active micromechanical air valve for a disk drive in accordance with the principles of the present invention includes a first layer having a first thermal coefficient of expansion, a second layer having a second thermal coefficient of expansion, wherein the first layer and the second layer are configured to form a membrane, the first and second layer engaging in a closed state to prevent air flow there between in a first thermal state and opening to allow air flow there between in a second thermal state.
Other embodiments of an active micromechanical air valve in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that the first thermal state is achieved by the absence of a control signal.
Another aspect of the present invention is that the control signal is a drive current from a current source.
Another aspect of the present invention is that the second thermal state is achieved by application of a control signal.
Another aspect of the present invention is that the control signal is a drive current from a current source.
Another aspect of the present invention is that the first layer is a conductive layer forming a bridge layer for conducting a drive current applied to the conductive layer.
Another aspect of the present invention is that the first layer further includes a nickel bridge.
Another aspect of the present invention is that the nickel bridge further includes a resistive, low stress insulating material sputtered thereon and a doped layer of polycrystalline silicon for providing an electrical resistive layer.
Another aspect of the present invention is that the second layer further includes a thermal expansive polymer.
Another aspect of the present invention is that the second layer further includes a first opening and a downward facing member and the first layer includes a second opening, the second opening of the first layer offset from the first opening in the second layer and the downward facing member plugging the second opening in the first layer when the first and second layer engage in the closed state to prevent air flow there between in the first thermal state.
In another embodiment of the present invention, a head for use in a disk drive is provided. The head includes a slider, a transducer formed on the slider, air tubes formed through the slider form the air bearing surface, a well formed at the back end of the slider, at least one air tube formed through the slider from the air bearing surface to the well for providing an air flow path from the air bearing surface of the slider to the back end of the slider and an active micromechanical air valve for fly height control of the head, including a first layer having a first thermal coefficient of expansion, a second layer having a second thermal coefficient of expansion, wherein the first layer and the second layer are configured to form a membrane, the first and second layer engaging in a closed state to prevent air flow there between in a first thermal state and opening to allow air flow between the air bearing surface and the membrane in a second thermal state.
In another embodiment of the present invention, a disk drive is provided. The disk drive includes at least one rotating disk for recording data, a housing, the rotatable disk being rotatably attached to the housing, an actuator arm assembly, coupled to the housing and at least one head, coupled to the actuator arm assembly, the at least one head writing and reading data to and from the at least one rotating disk, the at least one head, including a slider, a transducer formed on the slider, air tubes formed through the slider form the air bearing surface, a well formed at the back end of the slider, at least one air tube formed through the slider from the air bearing surface to the well for providing an air flow path from the air bearing surface of the slider to the back end of the slider and an active micromechanical air valve for fly height control of the head, including a first layer having a first thermal coefficient of expansion, a second layer having a second thermal coefficient of expansion, wherein the first layer and the second layer are configured to form a membrane, the first and second layer engaging in a closed state to prevent air flow there between in a first thermal state and opening to allow air flow between the air bearing surface and the membrane in a second thermal state.
In another embodiment of the present invention, a method of forming an active micromechanical air valve for fly height control of an air bearing slider is provided. The method includes forming a first layer having a first thermal coefficient of expansion, forming a second layer over the first layer having a second thermal coefficient of expansion, wherein the first layer and second layer are configured to form a membrane, the first and second layer engaging in a closed state to prevent air flow there between in a first thermal state and opening to allow air flow there between in a second thermal state.
In another embodiment, a valve may also be applied to an outer surface of the disk enclosure. This surface may also be to an intermediate chamber(s) attached to the outside of the disk enclosure. The use of a valve discussed herein can be used to regulate a pressure difference between the inside and outside of the disk drive.